U.S. patent number 5,723,932 [Application Number 08/665,237] was granted by the patent office on 1998-03-03 for dc motor with improved brushes and liquid pump using the same.
This patent grant is currently assigned to Nippondenso Co., Ltd.. Invention is credited to Motoya Ito, Takeshi Matsuda, Minoru Yasuda.
United States Patent |
5,723,932 |
Ito , et al. |
March 3, 1998 |
DC motor with improved brushes and liquid pump using the same
Abstract
A liquid pump has a DC motor and a pump in a cylindrical casing.
A pair of brushes are slidably contacted with a commutator of an
armature while being biased by springs. The specific resistance of
the positive brush is lower than the specific resistance of the
negative brush to enable the voltage drop at the brushes to be
decreased and motor efficiency to be increased without increasing
commutator wearing speed. The biasing force provided by the spring
biasing the positive brush is lower than the biasing force provided
by the spring biasing the negative brush.
Inventors: |
Ito; Motoya (Hekinan,
JP), Yasuda; Minoru (Chiryu, JP), Matsuda;
Takeshi (Anjo, JP) |
Assignee: |
Nippondenso Co., Ltd. (Kariya,
JP)
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Family
ID: |
26457166 |
Appl.
No.: |
08/665,237 |
Filed: |
June 17, 1996 |
Foreign Application Priority Data
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Jun 16, 1995 [JP] |
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7-148516 |
May 15, 1996 [JP] |
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8-119417 |
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Current U.S.
Class: |
310/248; 310/239;
310/245; 310/247; 310/251; 417/423.7 |
Current CPC
Class: |
F02M
37/08 (20130101); H01R 39/18 (20130101); H01R
39/381 (20130101); H02K 5/132 (20130101); H02K
13/10 (20130101) |
Current International
Class: |
F02M
37/08 (20060101); H02K 5/12 (20060101); H01R
39/38 (20060101); H02K 5/132 (20060101); H01R
39/18 (20060101); H02K 13/10 (20060101); H01R
39/00 (20060101); H02K 023/00 () |
Field of
Search: |
;417/423.7
;310/242,238,239,240,241,244,245,246,247,248,251,252 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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6-48377 |
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Apr 1985 |
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JP |
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3-7665 |
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Feb 1988 |
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JP |
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63-24972 |
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Feb 1991 |
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JP |
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Primary Examiner: Dougherty; Thomas M.
Assistant Examiner: Mullins; B
Attorney, Agent or Firm: Nixon & Vanderhye, P.C.
Claims
What is claimed is:
1. A direct current motor for a liquid pump comprising:
a casing;
an armature with a coil and a commutator at an end of the armature
in the casing;
positive and negative brushes arranged in the casing in slidable
contact with the commutator for supplying current to the
commutator; and
biasing springs for biasing the brushes onto the commutator,
wherein the brushes and the biasing springs are set to satisfy at
least one of the conditions of: (1) the positive brush has a lower
specific resistance than the negative brush's specific resistance
and (2) the biasing spring for the positive brush has a lower
biasing force than the negative brush biasing spring's biasing
force.
2. A liquid pump as in claim 1, wherein the negative brush and the
positive brush are substantially the same size.
3. A liquid pump comprising:
a DC motor including a casing, an armature with a coil and a
commutator at an end of the armature in the casing, at least a pair
of positive and negative brushes arranged in the casing in slidable
contact with the commutator for current supply to the commutator,
and biasing springs for biasing the brushes onto the commutator;
and
a pump driven by the DC motor for forcibly feeding liquid from one
end to another end in the casing,
wherein the positive brush has a specific resistance that is lower
than the negative brush's specific resistance.
4. A liquid pump as in claim 3, wherein:
the spring for the negative brush provides a biasing force that is
larger than the positive brush spring's biasing force.
5. A liquid pump as in claim 4, wherein:
the positive and negative brushes and the commutator are immersed
in a liquid.
6. A liquid pump as in claim 5, wherein the liquid is a fuel.
7. A liquid pump as in claim 3, wherein the negative brush and the
positive brush are substantially the same size.
8. A liquid pump comprising:
a DC motor including a casing, an armature with a coil and a
commutator at an end of the armature in the casing, a first brush,
and a second brush arranged in the casing in slidable contact with
the commutator for current supply to the commutator, and first and
second biasing springs for biasing the first and second brushes
onto the commutator, respectively; and
a pump driven by the DC motor for forcibly feeding liquid from one
end to another end in the casing,
wherein the first spring for biasing the first brush provides a
biasing force that is larger than a biasing force provided by the
second spring for biasing the second brush.
9. A liquid pump as in claim 8, wherein:
the first brush is a negative brush and the second brush is a
positive brush.
10. A liquid pump as in claim 9, wherein:
the positive brush has a specific resistance that is lower than the
negative brush's specific resistance.
11. A liquid pump as in claim 10, wherein:
the positive and negative brushes and the commutator are immersed
in a liquid.
12. A liquid pump as in claim 11, wherein the liquid is a fuel.
13. A liquid pump as in claim 9, wherein the negative brush and the
positive brush are substantially the same size.
14. A direct current motor for a liquid pump comprising:
an armature with a coil connected to a commutator;
a positive brush and a negative brush of substantially equal sizes,
both said brushes being in slidable contact with the commutator,
the positive brush having a lower specific resistance than the
negative brush's specific resistance; and
biasing springs for biasing the brushes onto the commutator, the
biasing spring for the positive brush having a lower biasing force
than the negative brush biasing spring's biasing force.
15. A liquid pump as in claim 14, wherein the negative brush, the
positive brush and the commutator are immersed in a liquid in
operation.
16. A liquid pump as in claim 15, wherein the liquid is a fuel.
17. A direct current motor having improved efficiency and reduced
commutator wear, said motor comprising:
an armature with a coil connected to a commutator;
a positive brush and a negative brush arranged in slidable contact
with the commutator, the positive brush having a lower specific
resistance than the negative brush's specific resistance; and
biasing springs for biasing the brushes onto the commutator, the
biasing spring for the positive brush having a lower biasing force
than the negative brush biasing spring's biasing force.
18. A direct current motor as in claim 17, wherein the negative
brush and the positive brush are substantially equal sizes.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electric direct current motor, and
more particularly, to a direct current motor for use in a liquid
pump which forcibly feeds fuel within a liquid tank to a liquid
consuming device.
2. Related Art
Various direct current (DC) motors for fuel pumps for internal
combustion engines are known well in the art such as Japanese
Utility Model Laid-Open Publication Nos. Hei 3-7665 and Sho
63-24972.
In Hei 3-7665, two sets of brushes having different specific
resistances are installed on a DC motor for a fuel pump. The brush
set having a high specific resistance is used when the engine does
not require a large amount of fuel. The electrical current flowing
to the DC motor is therefore reduced so as to reduce commutator
wear. Only when the engine requires a large amount of fuel, the
brush set having a low specific resistance is used to increase the
electrical current flowing to the DC motor.
In Sho 63-24972, the sliding contact area of the anode (i.e.,
positive) brush of one pair of commutator brushes having the same
specific resistance is larger than the sliding contact area of the
cathode (i.e., negative) brush. Thus, the electrical resistance of
the sliding contact surface between the anode brush and the
commutator is reduced, motor efficiency is improved and at the same
time commutator wear is reduced.
However, arrangement of the two sets of brushes having different
specific resistances as in Hei 3-7665 has disadvantages in that the
number of component parts is increased and the structure of the
brush holders becomes complicated.
In addition, forming the sliding contact area of the anode brush of
one pair of brushes larger than a sliding contact area of the
cathode brush as in Sho 63-24972 has a disadvantage in that the
fuel pump becomes larger in size due to an increased volume of the
brush holder.
SUMMARY OF THE INVENTION
The present invention has an object of solving the above described
disadvantages.
The present invention has another object of providing a direct
current motor capable of improving motor efficiency by restricting
commutator wear without increasing the number of component parts or
complicating the brush holder.
The present invention has a further object of providing a direct
current motor for a liquid pump such as a fuel pump.
According to the present invention, at least a pair of brushes are
slidably contacted by a biasing spring force towards a commutator
(and electrical current is supplied from the brushes to an armature
coil through the commutator). The specific resistance of the anode
brush is lower than the specific resistance of the cathode
electrode. Thus, a voltage drop caused by sliding contact between
the brushes and the commutator can be decreased without any
remarkable increase in the amount of electrical wear between the
anode brush and the commutator.
Preferably, the spring biasing force for the cathode brush is
larger than the spring biasing force for the anode brush.
More preferably, the anode brush, the cathode brush and the
commutator are immersed in liquid (such as fuel) so that mechanical
commutator wear is kept low compared with electrical commutator
wear. In the case of the fuel pump, fuel is forcibly fed from one
end within a casing to the other end by rotationally driving a vane
wheel or impeller by a rotating armature shaft within the
casing.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the present invention will become
more apparent from the following description when read with
reference to the accompanying drawings, in which:
FIG. 1 is a longitudinal sectional view showing an exemplary fuel
pump using a direct current motor according to one preferred
embodiment of the present invention;
FIG. 2 is a sectional view taken along a line II--II in FIG. 1;
FIGS. 3(a) and 3(b) are graphs showing electrical commutator
wearing speed caused by an anode brush and a cathode brush;
FIG. 4 is a graph showing the general relationship between
commutator wearing speed and electrical current versus spring
biasing force;
FIG. 5 is a graph showing motor efficiencies in the fuel pump of
the preferred embodiment; and
FIG. 6 is a longitudinal sectional view showing a modification in
arrangement of the commutator and the brushes in the fuel pump of
FIG. 1.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
Referring now to the drawings, preferred embodiments of the present
invention will be described below.
FIG. 1 is a sectional view showing a fuel pump using a direct
current motor according to one preferred embodiment of the present
invention. FIG. 2 is a sectional view taken along a line II--II in
FIG. 1.
In FIGS. 1 and 2, reference numeral 100 denotes a fuel pump as a
liquid pump. The fuel pump 100 is constructed such that a top cover
12 and a bottom cover 15 are integrally press fitted to each other
by a cylindrical casing 11. A direct current (DC) motor 20 and a
pump 30 are housed in the casing 11. The top cover 12 is formed
with a fuel discharge port 13 having a check valve 13a, and a
connector 14 for supplying electrical current to the DC motor 20.
In addition, the bottom cover 15 is formed with a fuel suction port
16 through which fuel is sucked and fed along the direction of
arrows shown in FIG. 1 and then discharged out of the discharge
port 13.
The DC motor 20 includes a pair of magnets 21a, 21b fixed to the
inner circumferential surface of casing 11 through motor housing
22. Armature 24 has a predetermined clearance with respect to
magnets 21a, 21b and has a longitudinally extending rotating shaft
23 at the radial center of the casing 11. The armature 24 includes
an armature coil 25 having a coil of wire wound around an iron core
and a disk-like commutator 26 to which each of the coil wire ends
of the coil part 25 is connected. The commutator disk is
perpendicular to rotating shaft 23 and is integrally formed with
resin into columnar member. The commutator 26 rotates while
slidably contacting a pair of brushes 27a, 27b guided by the motor
housing 22. Biasing forces are applied to the brushes by respective
springs 28a, 28b. The brushes are wired to the connector part 14.
As described later in detail, the brushes 27a, 27b have
respectively different specific resistances and the springs 28a,
28b have respectively different biasing forces.
The pump 30 is a regenerative pump. The pump includes a turbine
vane (impeller) 33 having at its outer circumference a vane 34
arranged between the bottom cover 15 within the casing 11 and a
pump cover 31 press fitted integrally with the casing 11. This
turbine vane 33 is engaged with an extended extremity of the
rotating shaft 23 in its rotating direction and fitted to it in
such a way that it may be axially slid.
The DC motor 20 of the present preferred embodiment is an 8-pole
motor. Its rotating shaft 23 is rotationally supported in a radial
direction by a bearing 29 fitted and installed at the motor housing
22 and a bearing 32 fitted and installed at the pump cover 31. The
rotating shaft 23 is supported in a thrust direction by an abutting
member 17 fixed to the bottom cover 15 and by the brush 27a,
27b.
Shown in FIGS. 3(a) and 3(b) are an experiment performed by the
present inventors as well as its results in order to measure actual
electrical wear caused by sparks generated between commutator 26
and brushes 27a, 27b when the fuel pump 100 according to this
embodiment is used. Since the fuel pump 100 in the preferred
embodiment of the present invention is operated while being
immersed in fuel, the commutator 26 and brushes 27a, 27b are also
always immersed in the fuel. Since it is known that mechanical wear
caused by friction between both members under this condition is
quite low as compared with electrical wear between them, the
mechanical wear in this case will not be considered.
In this case, if it is assumed that brushes 27a, 27b are slidably
contacted on the same circumference of the commutator 26 as shown
in FIG. 2, it is not apparent which one of the brushes, i.e., the
positive electrode (hereinafter merely defined as (+)) or the
negative electrode (hereinafter merely defined as (-)) causes more
or less electrical wear of the commutator 26. Accordingly, for the
experiment, the brushes having each of their contact surfaces cut
in an arcuate shape were manufactured in such a way that the brush
at the (+) electrode and the brush at the (-) electrode were placed
to slidably contact different circumferential areas on the
commutator 26. Two sets of brushes, i.e., one set of brushes having
each polarity was placed at an inner circumference and the other
set of brushes having each polarity was placed at an outer
circumference (e.g., because of different inner and outer
peripheral speeds, each of the combined units was evaluated).
FIG. 3(a) indicates commutator wearing speed when the brush of (-)
electrode is arranged at the inner circumference and the brush of
(+) electrode being arranged at the outer circumference. FIG. 3(b)
indicates commutator wearing speed when the brush at the (+)
electrode is arranged at the inner circumference and the brush at
the (-) electrode being arranged at the outer circumference.
As apparent from FIGS. 3(a) and 3(b), in either case, the
commutator wearing speed caused by the brush at the (-) electrode
is about three times the wearing speed caused by the brush at the
(+) electrode. Although the brush at the (+) electrode and the
brush at the (-) electrode were made of material having a
relatively high specific resistance in the prior art in order to
assure a service life of the commutator 26, in view of the above
described result, it is now seen to be possible to reduce the
voltage drop at the brush at the (+) electrode while still
maintaining full brush set service life by setting a lower specific
resistance at the brush of the (+) electrode than a specific
resistance of the brush at the (-) electrode.
In addition, the spring biasing force at either the brush at the
(+) electrode or the brush at the (-) electrode was changed to see
what kind of influence was caused by the biasing forces of the
springs to both electrical wearing and electrical current of the
commutator 26. As shown in FIG. 4, it became apparent that an
increase in the spring biasing force enables commutator wearing
speed to be decreased and, in turn, this enables electrical current
to be increased. Accordingly, it is possible to permit an increase
in electrical current while also restricting commutator wearing
speed by increasing the biasing force of only the spring at the (-)
brush--thus substantially influencing against the excessive
commutator wearing speed otherwise to be expected at the (-)
brush.
Here, in this experiment, each cross sectional area of the brushes
at the (+) electrode and the (-) electrode in the prior art product
and the present preferred embodiment is 0.224 square centimeters,
respectively. It is assumed that increased biasing force caused
contact pressure of the brush against the commutator to be
increased, resulting in a reduction of electrical sparks between
the brush and the commutator and, as a consequence, the commutator
wearing speed was decreased. In addition, it is assumed that
increased contact pressure caused the contact resistance to be
reduced and this caused the electrical current to be increased.
In response to the results of the foregoing experiments, the
specific resistance of the brush at the (+) electrode of the
brushes 27a, 27b is preferably made lower than the specific
resistance of the brush at the (-) electrode. Further, the spring
biasing force for the brush at the (-) electrode of the springs
28a, 28b preferably made larger than the spring biasing force of
the brush at the (+) electrode. With such an arrangement, as shown
in FIG. 5, it becomes possible to improve motor efficiency of the
present preferred embodiment as compared with that of the prior
art.
In the prior art product in the experiment, the specific resistance
of the brushes was 1,000 .mu..OMEGA.cm for both (+) electrode and
(-) electrode and the biasing force of the brush springs was 150 g.
In the presently preferred embodiment in the experiment, the brush
specific resistance for the (+) electrode was 2,000 .mu..OMEGA.cm
while the brush specific resistance for the (-) electrode was
10,000 .mu..OMEGA.cm, and the biasing force of the brush spring for
the (+) electrode was 150 g while the biasing force of the brush
spring for the (-) electrode was 350 g.
As described above, at the DC motor 20, a pair of brushes 27a, 27b
are slidably contacted with the disk commutator 26 arranged at the
end of armature 24 through the biasing forces of springs 28a, 28b.
An electrical current is supplied from the brushes 27a, 27b to the
coil 25 of the armature 24 through the commutator 26. The fuel at
the pump 30 is forcibly fed from the suction port 16 at one end
within the casing to the discharge port 13 at the other end under
rotational driving of the vane wheel including turbine vane 33
driven by the rotating shaft 23 of the armature 24 within the
casing 11. The specific resistance of the brush at the (+)
electrode in these brushes is set to be lower than the specific
resistance of the brush at the (-) electrode. Therefore, it is
possible to reduce the voltage drop caused by the sliding contact
without causing a large electrical commutator wearing rate between
the brush at the (+) electrode and the commutator. Due to this
fact, it is possible to restrict wearing of the commutator or to
improve motor efficiency without increasing the number of component
parts of the fuel pump or making a complex structure of the brush
holder.
Further, at the DC motor 20, a pair of brushes 27a, 27b arranged at
the casing 11 are slidably contacted with the commutator 26
arranged at the end of armature 24 through the biasing forces of
springs 28a, 28b. An electrical current is supplied from brushes
27a, 27b to the coil 25 of the armature 24 through the commutator
26. The fuel at the pump 30 is forcibly fed from the suction port
16 at one end within the casing to the discharge port 13 at the
other end under rotational driving of the vane wheel including
turbine vane 33 driven by the rotating shaft 23 of the armature 24
within the casing 11. The biasing force of the spring at the brush
of the (-) electrode of these springs 28a, 28b is set to be larger
than the biasing force of the spring at the brush of the (+)
electrode. Therefore, it is possible to reduce the commutator
wearing rate with the brush at the (-) electrode and to restrict an
increase of electrical current. Due to this fact, it is possible to
restrict wearing of the commutator and to improve motor efficiency
without making a complex structure of the brush holder.
In addition, since the liquid pump (e.g., a fuel pump) is immersed
in the liquid (e.g., fuel), mechanical wear caused by friction
between both the brushes 27a, 27b immersed in the fuel and the
commutator 26 is quite low as compared with electrical wear. Due to
this fact, the liquid pump in which the brushes 27a, 27b and the
commutator 26 are immersed in the liquid enables a service life of
the commutator or the like to be remarkably improved merely by
providing a countermeasure against electrical wearing.
In the foregoing preferred embodiment, the commutator 26 is
arranged like a disk in a direction perpendicular to the rotating
shaft 23 of the armature 24 and the DC motor 20 supplied with
electricity through the brushes 27a, 27b biased by the springs 28a,
28b. However, it may be modified to a liquid pump such as a fuel
pump 100', as shown in FIG. 6, in which a commutator 26', is
arranged coaxially to the rotating shaft 23', of an armature 24'
and in a cylindrical manner. A DC motor 20', is supplied with
electric current through brushes 27a', 27b', biased by springs
28a', 28b' in the radial direction.
In addition, although the DC motor of the present invention has
been applied to the regenerative type pump in the preferred
embodiment, it may also be applied to various types of pumps, e.g.,
geared pumps or vane pumps.
Further, the present invention may be modified in many other ways
without departing from the spirit of the invention.
* * * * *